Field of the Invention
Embodiments of the present invention relate to a semiconductor device, and more particularly relates to a semiconductor device including a plurality of memory cells in which a refresh operation is necessary to retain information.
Description of Related Art
In a volatile memory device of a charge retention type represented by a DRAM (Dynamic Random Access Memory), it is necessary to cyclically execute a refresh operation as recharging in order to retain data of memory cells. The cycle of executing the refresh operation is decided based on a period in which the memory cells can retain data (hereinafter referred to as “a data retention period”).
In recent years, in view of reducing power consumption of the semiconductor device, it is desired that the cycle of executing a refresh operation is extended as long as possible. For example, Japanese Patent Application Laid-open No. H7-296582 focuses on a relationship between a temperature and a data retention period and discloses a semiconductor device that changes the cycle of executing a refresh operation according to values indicated by a temperature sensor.